SJL/J lymphomas can be used as a model of tumor progression from a slow-growing malignancy to an aggressive tumor. We have previously shown that one of the class I MHC antigens, D[unreadable]s[unreadable], is not expressed in some SJL/J lymphomas. The D[unreadable]s[unreadable]-negative tumors are not rejected and grow rapidly. The goal of this research is to determine the structural defect(s) that prevents expression of the D[unreadable]s[unreadable] antigens. Loss of expression could be due to gross deletion or rearrangement of the gene or small alterations such as point mutations or gene conversion. We will identify and sequence genomic D[unreadable]s[unreadable] genes from normal tissue and from several malignant SJL/J lymphoma lines. A comparison of the sequences will locate the gene(s). Since the amino acid sequence of the D[unreadable]s[unreadable] glycoprotein is not known, the D[unreadable]s[unreadable] gene(s) must be identified from the other 33-35 cross-hybridizing class I genes. A combination of two approaches will be used to identify and determine the number of D[unreadable]s[unreadable] genes: (1) several cDNA probes will be made from mRNA isolated by immunopurification of polysomes. Size-selected, double-stranded cDNA will be used for insertion into pBR322. These cDNA clones will be tested for their ability to cross-hybridize with a class I probe and then will be sequenced; and (2) the genomic D[unreadable]s[unreadable] gene(s) will be identified from the other 33-35 cross-hybridizing class I genes on a Southern blot by comparing the DNA from various H-2 congenic and intra-MHC recombinant mouse strains as well as from many SJL/J lymphoma lines. The D[unreadable]s[unreadable] gene(s) will be identified by its "unique" restriction enzyme site polymorphism. This gene(s) will be cloned into a cosmid vector for sequence analysis. The identify of the genomic D[unreadable]s[unreadable] gene(s) will be confirmed by cloning the appropriate restriction fragment(s) containing the D[unreadable]s[unreadable] gene(s) and comparing the sequence of the genomic gene(s) with the D[unreadable]s[unreadable] cDNA sequence(s). The D[unreadable]s[unreadable] genes will be subcloned into the pSV2-neo vector for both sequence and immunochemical analyses. Immunochemical analyses of the glycoproteins produced in transformed mouse L cells will confirm the production of clones containing the D[unreadable]s[unreadable] gene(s). Defective D[unreadable]s[unreadable] genes will then be cloned from various SJL/J lymphoma lines and sequenced. Such alterations in gene structure may be detected by restriction site analyses on Southern blots followed by sequencing of the appropriate segment of the tumor D[unreadable]s[unreadable] gene. These studies will, therefore, identify the genetic mechanisms that prevent the expression of cell surface antigens in malignancies. (AG)